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The Xerces Blue (Glaucopsyche xerces) is considered to be the first butterfly to become
extinct in historical times. It was notable for its chalky lavender wings with conspicuous white spots
on the ventral wings. The last individuals were collected in their restricted habitat, in the dunes
near the Presidio military base in San Francisco, in 1941. We sequenced the genomes of four 80- to
100-year-
old
Xerces Blue, and seven historical and one modern specimens of its closest relative,
the Silvery Blue (Glaucopsyche lygdamus). We compared these to a novel annotated genome of
the Green-Underside
Blue (Glaucopsyche alexis). Phylogenetic relationships inferred from complete
mitochondrial genomes indicate that Xerces Blue was a distinct species that diverged from the
Silvery Blue lineage at least 850,000 years ago. Using nuclear genomes, both species experienced
population growth during the Eemian interglacial period, but the Xerces Blue decreased to a very
low effective population size subsequently, a trend opposite to that observed in the Silvery Blue.
Runs of homozygosity and deleterious load in the former were significantly greater than in the later,
suggesting a higher incidence of inbreeding. These signals of population decline observed in Xerces
Blue could be used to identify and monitor other insects threatened by human activities, whose
extinction patterns are still not well known.
Citació
eLife, núm. 12:RP87928 (2024), p.1-21